Wireless communication method and apparatus for implementing access point startup and initial channel selection processes

ABSTRACT

A startup process of an access point (AP) includes a discovery phase and an announcement phase. During the discovery phase, the AP detects neighboring APs from its own extended service set (ESS), neighboring APs from different ESSs, and external sources of interference. During the announcement phase, the AP transmits its beacon signals at maximum power in order to accelerate recognition by neighboring APs running the discovery phase. An automatic initialization channel selection process of an AP scans channels the AP will use to communicate. Information of each scanned channel is recorded and a best performance channel is determined for use by the AP.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/256,521, filed Oct. 23, 2008, which issued as U.S. Pat. No. 7,558,571on Jul. 7, 2009, which is a continuation of U.S. patent application Ser.No. 11/332,973, filed Jan. 17, 2006, which issued as U.S. Pat. No.7,454,205 on Nov. 18, 2008, which is a continuation of U.S. patentapplication Ser. No. 10/978,956, filed Nov. 1, 2004, which issued asU.S. Pat. No. 7,016,684 on Mar. 21, 2006, which claims the benefit ofU.S. Provisional Patent Application No. 60/526,134, filed on Dec. 1,2003, U.S. Provisional Patent Application No. 60/535,019, filed on Jan.8, 2004, and U.S. Provisional Patent Application No. 60/535,073, filedon Jan. 8, 2004, which are incorporated by reference as if fully setforth.

FIELD OF INVENTION

The present invention relates to a wireless communication system. Moreparticularly, the present invention relates to initializing operatingparameters and selecting the most appropriate operating channel for anaccess point (AP).

BACKGROUND

The conditions of a radio link under which a wireless communicationsystem operates may change at any time. Since a wirelesstransmit/receive unit (WTRU) is mobile, the WTRU may be out-of-range, orwithin range of one or more APs depending upon the position of the WTRU.When an AP is newly established, or powers up again after powering downfor some reason, the startup process of the AP must evaluate its radioresource environment. Typically, the startup process also provides amechanism for announcing itself to other APs of its own extended serviceset (ESS) such that the other APs can self-adjust their own operatingparameters accordingly.

There are several current schemes that are employed in order to increasethe capacity of a wireless communication system. Channel, i.e.,frequency, selection is one of such schemes, whereby one or more APs ina network select one or more channels to communicate with theirassociated WTRUs. Coordination of AP channel selection is usuallyperformed manually. However, it is very impractical to manuallycoordinate channel selection in response to every small change in thenetwork configuration since it may cause a redesign and reconfigurationof all APs. Unlicensed spectra and external sources of interference alsoraise problems that are not adequately addressed by manual coordination.Moreover, it is difficult for manual channel selection to assignchannels such that the traffic loads of neighboring APs are shared amongthe available channels in a way that maximizes overall system capacity.

Another problem with prior art schemes is encountered when multiple APsattempt to power-up simultaneously. When this occurs within a network,all of the APs try to make a channel selection at the same time. Thus,the channel selection by the APs would not be optimal since each AP doesnot take into account the channel selection of neighboring APs.

A method and system which overcomes the above-mentioned problems wouldbe greatly beneficial.

SUMMARY

The present invention provides a method and apparatus for implementingstartup and initial channel selection processes for an AP.

The startup process of the AP includes a path loss discovery phase andan announcement phase. During the path loss discovery phase, the APdetects neighboring APs from its own ESS, neighboring APs from differentESSs, and external sources of interference. During the announcementphase, the AP transmits a beacon signal in order to acceleraterecognition by neighboring APs also running the path loss discoveryphase. The startup process provides the AP with the ability to monitorand evaluate its radio environment, and therefore allows the AP toself-determine initial operating parameters.

An initialization channel selection process for an AP is automaticallyimplemented when the AP's startup process begins.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description, given by way of example and to be understood inconjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of a wireless communication system inaccordance with the present invention;

FIG. 2 is a flow diagram of a startup process of an AP according to oneembodiment of the present invention;

FIG. 3 is a flow diagram of an automatic channel selection processaccording to another embodiment of the present invention; and

FIG. 4 is a flow diagram of an initialization channel selection processin accordance with yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the terminology “WTRU” includes but is not limited to a userequipment (UE), mobile station, fixed or mobile subscriber unit, pager,or any other type of device capable of operating in a wirelessenvironment.

Hereinafter, the terminology “AP” includes but is not limited to anaccess point, a base station, Node-B, site controller, or any other typeof interfacing device in a wireless environment.

The features of the present invention may be incorporated into an IC orbe configured in a circuit comprising a multitude of interconnectingcomponents.

The present invention as described herein, is generally applicable towireless local area network (WLAN) technologies, as applied to the IEEE802.11 and ETSI HyperLAN specifications in general, but is envisaged tobe applicable to other interference-limited wireless systems such asIEEE 802.15 and IEEE 802.16.

FIG. 1 is a block diagram of a wireless communication system 100according to the present invention. The wireless communication system100 comprises an AP 105 and a plurality of WTRUs 110 a-110 n. The AP 105communicates with the WTRUs 110 a-110 n over a wireless link 115 via anantenna 120. The AP 105 includes a transceiver 125, a channel selector130, a measuring unit 135, a power controller 140, a timer 145 and amemory 150. The transceiver 125 transmits signals 115 a-115 n to, andreceives signals 115 a-115 n from, the WTRUs 110 a-110 n via the antenna120.

The channel selector 130 selects a channel which is used forcommunication with each WTRU 110 a-110 n. The measuring unit 135measures operating parameters for supporting the AP 105. The measuringunit 135 is responsible for collecting, processing and storing channelmeasurements including, but not limited to: the channel utilization(i.e., percentage of time that the channel is busy), the level ofexternal (non 802.11) interference, the received signal strengthmeasured on received packets, and the like. The power controller 140controls the transmission power of the AP 105. The timer 145 sets one ormore predetermined periods during which the AP 105 performs certainoperations. The memory 150 provides storage for the AP 105, includingrecording data such as results of the measurements.

FIG. 2 is a flow diagram of a startup process 200 of the AP 105including a discovery phase 210 and an announcement phase 220. In thediscovery phase 210, the AP 105 initializes its measurement parametersand values (step 211). The measurement parameters and values that areinitialized may, for example, include the parameters and values listedin the following Table 1. As those of skill in the art would realize,other parameters and values may be used, in addition to, or in place of,these parameters and values.

TABLE 1 Symbol Description Type Default value ACS Allowable Channel SetConfiguration {1, 6, 11} parameter T_(mpp)_fix^(Discover) Discoveryphase value of the Configuration 1000 ms fixed component of the Silentparameter Measurement Period generation interval T_(mpp)_var^(Discover)Discovery phase value of the Configuration 0 ms amplitude of thevariable parameter component of the Silent Measurement Period generationinterval T_(mpp)_dur^(Discover) Discovery phase value of theConfiguration 1000 ms duration of a Silent Measurement parameter PeriodN_(MIN)_MS^(Discover) Minimum number of Configuration 4 measurement setsduring the parameter Discovery Phase N_(MAX)_MS^(Discover) Maximumnumber of Configuration 15 measurement sets during the parameterDiscovery phase T_(dur) ^(Announce) Announcement phase durationConfiguration 10 seconds parameter T_(beacon) ^(Announce) Beacontransmission period Configuration 100 ms during Announcement phase.parameter P_(MAX) Maximum AP transmission Configuration 20 dBm powerparameter

In step 212 of the discovery phase 210, the measuring unit 135 measuresthe operating parameters by performing N_(meas) _(—) _(sets) ^(Discover)measurement sets, whereby measurements are taken sequentially on eachchannel in an allowable channel set (ACS) for a period of time during ameasurement set which consists of a complete cycle of measurementperiods through all channels in the ACS. The operating parameters, forexample, may be the transmission power and the channel setting of the AP105. It is preferable that the overall measurement duration on eachchannel, which corresponds to T_(mpp) _(—) _(fix)^(Discover)×N^(Discover), is set such that enough loud packets arereceived from neighboring APs. The loud packets are the packets that aresent at maximum power by an AP to increase the likelihood of its beingdetected by its neighboring APs.

The duration of T_(mpp) _(—) _(fix) ^(Discover) is set such that it islong enough to limit edge effects, which occur when a packet is intransmission during transition between measurement periods (MPs). It isalso preferable for the T_(mpp) _(—) _(fix) ^(Discover) to be set to aduration short enough to allow continuous cycling between frequencies sothat the AP 105 can detect a channel change by one of its neighbors. Theduration and periods are determined by the timer 145. The duration ofthe discovery phase 210 consists of a random number of measurement sets,uniformly distributed between N_(MIN) _(—) _(MS) ^(Discover) and N_(MAX)_(—) _(MS) ^(Discover). The duration of the discovery phase 210 israndom to account for the case where two or more APs are powered-upsimultaneously, avoiding that initial frequency selection be performedat the same time for these APs.

As a result of these measurements, the AP 105 can determine its radioenvironment, such as a detection of neighboring APs from its own ESS, adetection of neighboring APs from different ESSs, and a detection ofexternal sources of interference.

Referring back to FIG. 2, once the N_(meas) _(—) _(sets) ^(Discover)performance measurement sets have been completed (step 212), the powercontroller 140 invokes power control for the AP 105 (step 213). Thepower control determines a baseline range of the AP 105 and a relatedbaseline power setting. After the power control of the AP 105 is invokedat step 213, the channel selector 130 invokes a channel optimizationprocess (step 214) to select channels that a particular AP or network ofAPs use. The initial channel setting of the AP 105 is determined basedon parameters that are determined by the power controller 140.

During the discovery phase 210, the AP 105 remains silent (i.e., the AP105 does not transmit any packets). Upon completion of the discoveryphase 210, the AP 105 has gathered enough information to determine anoptimal operating channel and select a transmission power setting.

After the discovery phase 210 ends, an announcement phase 220 follows.During the announcement phase 220, the AP configures its operatingchannel to the optimal channel determined at the end of the discoveryphase 210. It should be noted that other processes may be performed inthe interim as necessary. The purpose of the announcement phase 220 isto accelerate the detection of the AP by its neighboring APs. In thebeginning of the announcement phase 220, various parameters, (e.g.,T_(dur) ^(Announce), T_(beacon) ^(Announce), P_(Max)), and areinitialized (step 221). During the announcement phase duration T_(dur)^(Announce), the AP 105 only transmits beacon frames having a maximumtransmission power P_(Max) with period T_(beacon) ^(Announce) (step222). This accelerates the detection of the AP 105 by other APs, becauseonly maximum power packets are transmitted. During the announcementphase 220, WTRUs beyond the coverage range of the AP 105 may attempt toassociate with the AP 105, because the AP 105 is transmitting at itsmaximum power. For this reason, all association requests from WTRUs aredenied during the announcement phase 220 in order to avoid associating aWTRU that will be out of range during normal operation.

Once the announcement phase 220 ends, the startup of the AP 105 iscomplete. The AP 105 then configures itself for its normal operation(step 223) and begins normal operation (step 230). The AP 105 sets itstransmission power to the setting determined by the power controller140, after which the AP 105 begins normal operation and starts acceptingassociation requests from the WTRUs 110.

FIG. 3 is a flow diagram of an automatic initialization channelselection process 300 according to one embodiment of the presentinvention. In the preferred embodiment, the channel selection process isinvoked at the end of the discovery phase 210, where measurements oneach channel have been taken. Channels are chosen for use by aparticular AP, or a network of APs. Channel selection can be done eithermanually or automatically, and can be initiated at deployment orperformed dynamically during operation. The present invention may beimplemented in conjunction with wireless local area network (WLAN)applications, e.g., in accordance with IEEE 802.11.

The initialization channel selection process 300 is performed during thestartup process 200 and determines the best operation channel. In thepreferred embodiment, channels are being scanned during the discoveryphase 210. At the end of the discovery phase 210, the channels selectionprocess is invoked in step 214 to select the best channel based on themeasurements observed on each channel during the discovery phase 210. Inall cases, the initialization channel selection process 300 scans aplurality of channels (e.g., channels 1-11) to detect the best channelavailable. The sequence of scanned channels may be in a predeterminedorder, or it may be random. The channel sequence does not need toinclude all available channels. For each channel scanned, the processdetermines: (1) what other APs are operating on that channel; (2)whether the APs are part of the same system, (i.e., according to theESS); (3) the signal strength of the APs; (4) the amount of traffic onthe channel; and (5) if there are any other sources of interference onthe channel (e.g., non-802.11 interference) and the received power levelon non-WLAN interference. After the scanning is complete, the AP cancalculate which channel would give the best performance (e.g., thechannel that has the least amount of interference). The AP then retunesitself to that channel. Depending on whether the other APs detected arepart of the same system, the AP can decide to be more or less aggressivein the choice of channel to use.

In an alternate embodiment, coordinated frequency selection may beaccomplished by: (1) having APs exchange information with each otherabout their properties (e.g. load, capabilities or position); or (2)having a centralized scheme that can obtain information from each AP,and setting the channel of all APs in the network. For the first case,the decision is still made autonomously by each AP, but the informationexchanged can allow a better decision (e.g., it can include statisticsthat are difficult to observe externally by another AP). For the secondcase, information is gathered from the different APs and communicated toa centralized unit or device, which upon reception of the informationtakes a decision and communicates the decision back to the differentAPs.

Referring still to FIG. 3, when the initialization channel selectionprocess 300 is initiated (step 305), the AP 105 is allowed to scan allchannels to detect the identity and a received signal strength indicator(RSSI) of all APs in the vicinity (step 310). In the preferredembodiment, step 310 may be implemented during the discovery phase 210.In step 315, the channel list is scanned. All, or a portion, of thelisted channels may be sequentially scanned in a predetermined or randomorder. Information associated with each AP detected on each channel isrecorded (step 320). This information may include, but is not limitedto, the identity of other APs which are operating on the scannedchannel, an indication of whether other APs are part of the same ESS,the signal strength of the APs, the amount of traffic on the channel andwhether there are any other sources of interference on the channel.

After the scanning is complete, the AP 105 determines which channelprovides the best performance (step 325). This may be determined, forexample, by measuring which channel has the least amount of interferenceor whether other APs are part of the same ESS. Once the channel havingthe best performance is determined, the AP 105 tunes itself to the bestchannel.

FIG. 4 is a detailed flow diagram of an initialization channel selectionprocess 400 used to determine the best channel upon AP startup accordingto another embodiment of the present invention. The initializationchannel selection process 400 includes a candidate channel determinationprocess 405 and a channel selection process 450.

In the candidate channel determination process 405, the AP 105 retrievesthe maximum allowed interference I_(MAX) (step 410), which is themaximum allowed interference on any given channel determined based onthe baseline range of an AP. I_(MAX) may be obtained from the powercontrol process. I_(MAX) is calculated by the initialization channelselection process 400 using Equation (1) below. Some of the parametersthat are used in Equation (1) are retrieved from the power controlprocess. Specifically, power control will determine RNG_(base). P_(MAX),(C/I)_(req) _(—) _(high) and M₁ on the other hand are pre-determinedparameters. Preferably, I_(MAX) for the candidate channel determinationprocess 405 is calculated based on Equation (1) as follows:

I _(MAX) =P _(MAX) −RNG _(base)−(C/I)_(req) _(—) _(high) −M ₁;  Equation(1)

where P_(MAX) is the maximum transmission power of the AP 105;RNG_(base) is the range covered by the AP 105; and (C/I)_(req) _(—)_(high) is the required carrier power-to-interference ratio of a highrate packet, (for example 11 Mbps). M₁ is a margin to eliminate channelswith interference levels too close to the actual maximum allowed level.Alternatively, a pre-determined value of I_(MAX) may be used todetermine the list of candidate channels.

A first channel is selected from an ACS (step 415). Interference I of achannel is measured and compared with the maximum allowed interferenceI_(MAX) (step 420). If the interference I of the channel is less thanthe maximum allowed interference I_(MAX), the AP 105 records the channelin a candidate list in the memory 150 (step 425). If the interference Iof the channel is not less than the maximum allowed interferenceI_(MAX), the AP 105 checks whether any more channels in the ACS exists(step 430). If more channels in the ACS exist, the AP 105 selects nextchannel from the ACS (step 435) and the candidate channel determinationprocess 405 then returns to step 420.

If no more channels exist in the ACS, the AP 105 checks whether anycandidate channel is available (step 440). If, in step 440, it isdetermined that no candidate channel is available, the AP 105 increasesI_(MAX) by ΔdB (step 445) and the candidate channel determinationprocess 405 returns to step 415. If, in step 440, it is determined thatat least one candidate channel exists, the candidate channeldetermination process 405 is complete and the channel selection process450 is then performed.

One criterion used by the channel selection process 450 is the number ofneighboring BSSs that have been detected on each channel N_(B)(k). Oncethe candidate channels are selected, the minimum number of detectedbeacons from different BSSs, among all candidate channels, N_(B) ^(MIN)is determined (step 455). The number of neighboring BSSs that have beendetected on channel k, N_(B)(k), is compared with the minimum number ofdetected BSSs, N_(B) ^(MIN), and all channels for which N_(B)(k)>N_(B)^(MIN) are removed from the list of candidate channels (step 460). Inother words, only the channels with the minimum number of detected BSSsare retained. Alternatively, in steps 455 and 460, the number ofdetected neighbor BSSs on each channel could be replaced with thechannel utilization on each channel. The channel utilization measurementcorresponds to the percentage of time that the receiver is carrierlocked by a WLAN signal. In this case, the channel selection processwould favor channels that have lower channel utilization.

Another criterion used by the channel selection process is the minimummeasured interference level, which is determined among all remainingcandidate channels (step 465). The minimum measured interference levelon channel k I(k) and the minimum interference level I_(MIN) arecompared, and all channels for which I(k)>I_(MIN) from the list ofcandidate channels are removed (step 470). In other words, only thechannels with the minimum interference level are retained.

If more than one candidate channel with the minimum interference levelexists, a channel is randomly selected among the remaining candidatechannels (step 475).

Exemplary parameters of the initialization channel selection process arelisted in the following Table 2. As those of skill in the art wouldrealize, other parameters and values may be used in addition, or inplace of, these values.

TABLE 2 Default Symbol Description Type Value ACS Allowable channel set.Configuration {1, 6, 11} parameter N_(B)(k) The number of neighboringBSSs Measurement NA detected on channel k. The minimum value of EDT isused to detect neighboring beacon frames. I(k) The interference measuredon Measurement NA channel k. I is measured as the average receivedsignal power in the absence of “carrier lock” by the receiver (i.e. thereceiver is not receiving any packets). RNG_(base) Baseline Range (setby the Path Internal NA Loss Discovery process) parameter (C/I)_(req)Minimum required carrier power to Configuration 10 dB interference ratioto support parameter maximum data rate. P_(MAX) Maximum AP transmissionpower Configuration 20 dbm parameter I_(MAX) The maximum allowedinterference Internal NA on any given channel determined parameter basedon baseline range. M_(I) Interference margin used in the Configuration 3dB calculation of the maximum parameter allowable interference level,I_(MAX) Δ The amount, in dB, by which the Configuration 3 dB maximumallowed interference, Parameter I_(MAX), is increased if there are nocandidate channels for which I < I_(MAX).

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone or in various combinations with orwithout other features and elements of the present invention.

1. A method of optimizing the selection of channels used by an accesspoint (AP), the method comprising: the AP determining a plurality ofcandidate channels, wherein the candidate channels are chosen from anallowable channel set (ACS) on a condition that a detected interferenceof each candidate channel does not exceed an established maximum allowedinterference; determining a number of beacons detected on each of thecandidate channels; and selecting at least one of the candidate channelson which a smallest number of beacons was detected and on a conditionthat there are at least two candidate channels which have aninterference level that does not exceed a predetermined minimuminterference level.
 2. The method of claim 1 wherein on a condition thatmore than one candidate channel is selected, the method furthercomprising: measuring an interference level on each of the selectedcandidate channels; and selecting at least one of the selected candidatechannels having an interference level that does not exceed thepredetermined minimum interference level.
 3. An access point (AP)comprising: the AP configured to: determine a plurality of candidatechannels; determine a number of beacons detected on each of thecandidate channels; and a channel selector configured to: select atleast one of the candidate channels on which a smallest number ofbeacons was detected; and select at least one of the candidate channelsrandomly on a condition that there are at least two candidate channelswhich have an interference level that does not exceed a predeterminedminimum interference level.
 4. The AP of claim 3 further comprising: ameasuring unit configured to measure an interference level on each ofthe candidate channels selected by the channel selector on a conditionthat more than one candidate channel is selected; and the channelselector is further configured to select at least one of the candidatechannels having a measured interference level that does not exceed thepredetermined minimum interference level.